Neuregulin (NRG; heregulin, HRG), also known as glial growth factor (GGF) and new differentiation factor (NDF), is a kind of glycoprotein with a molecular weight of 44 KD. As the ligand of tyrosine kinase receptor of ErbB family, neuregulin is responsible for cell signaling. NRG family has four members: NRG1, NRG2, NRG3 and NRG4 (Falls et al., Exp Cell Res. 284:14-30,2003). NRG1 plays an important role in nervous system, heart and breast. It is also evidenced that NRG1 signal transmission plays a part in the development and function of other organ systems, as well as in the pathogenesis of human diseases (including schizophrenia and breast cancer). NRG1 has many isomers. The research in gene mutated mice (gene knock-out mice) indicates that isomers with different N terminal region or EGF-like domain have different in vivo functions. The present invention is based on NRG-1β.
NRG-1β is a transmembrane protein (Holmes et al., Science 256, 1205-1210,1992). The extracellular region is N terminal region, comprising immune globulin like domain (Ig-like domain) and EGF-like domain. The intracellular region is C terminal region. Under the action of extracellular matrix metalloproteinase, the extracellular region of NRG is in a free state after being cut off by enzyme, thus facilitate binding to ErbB3 receptor on the cell surface and activating relevant cell signal transmission.
EGF receptor family can be divided into four classes, including ErbB1, ErbB2, ErbB3 and ErbB4, all of which are transmembrane proteins with a molecular weight of around 180-185 KD. They all comprise an extracellular ligand-binding domain in N terminal region except ErbB2. They all have protein tyrosine kinase activity in intracellular C terminal region except ErbB3. ErbB1 is epidermal growth factor receptor while ErbB3 and ErbB4 are neuregulin receptors. Among these neuregulin receptors, only ErbB2 and ErbB4 are highly expressed in heart (Yarden et al., Nat Rev Mol Cell Biol, 2: 127-137,2001).
After NRG binds to the extracellular domain of ErbB3 or ErbB4, it induces the formation of heterodimers of ErbB3, ErbB4 with other ErbB receptors (normally including ErbB2) or homodimer of ErbB4, which results in phosphorylation of the receptor's intracellular region (Yarden et al., Nat Rev Mol Cell Biol, 2: 127-137,2001). The phosphorylated intracellular domain then binds signaling proteins inside the cell, thus activating the downstream AKT or ERK signaling pathway, and inducing a series of cell reactions, such as stimulation or depression of cell proliferation, cell apoptosis, cell migration, cell differentiation or cell adhesion.
NRG plays an particularly important role in the development of heart (WO0037095, CN1276381, WO03099300, WO9426298, U.S. Pat. No. 6,444,644, WO9918976, WO0064400, Zhao et al., J. Biol. Chem. 273, 10261-10269, 1998). At the early stage of embryo development, the expression of NRG is limited in endocardium, whereafter it is released to periphery myocardial cell by paracrine and binds to the extracellular domain of protein tyrosine kinase receptors ErbB4 on cytomembrane, the ErbB4 than forms a heterodimer with ErbB2. The formation and activation of the ErbB4/ErbB2 complex is essential to form the trabecular of sponge-like heart at early phase. The absence of any of the three protein genes for NRG proteins, ErbB4 and ErbB2, would lead to an embryo without trabecular and death in uterus at early development. WO0037095 shows that a certain concentration of neuregulin could sustainably activate ERK signaling pathway, promote the differentiation and growth of myocardial cells, guide the reconstruction of sarcomere and cytoskeleton at the site where myocardial cells are adhered to cells, improve the structure of myocardial cells and enhance myocardial cell contraction. WO0037095 and WO003099300 also indicate that NRG could be used in the detection, diagnosis and treatment of various cardiovascular diseases.
The following is a list of some prior art technical literature related to the present invention: 1. Cardiac muscle function and manipulation:WO0037095; 2. New application of neuregulin and its analogs: CN1276381; 3. Neuregulin based methods and composition for treating cardiovascular diseases: WO03099300; 4. Zhao Y Y, Sawyer D R, Baliga R R, Opel D J, Han X, Marchionni M A and Kelly R A. Neuregulins PromoteSurvival and Growth of Cardiac Myocytes. J. Biol. Chem. 273, 10261-10269 (1998); 5. Methods for treating muscle diseases and disorder: WO9426298; 6. Methods of increasing myotube formation or survival or muscle cell mitogenesis, differentiation or survival using a neuregulin: U.S. Pat. No. 6,444,642. 7. Therapeutic methods comprising use of a neuregulin: WO9918976; 8. Methods for treating congestive heart failure: WO0064400; 9. Holmes W E, Sliwkowski M X, Akita R W, Henzel W J, Lee J, Park J W, Yansura D, Abadi N, Raab H, Lewis G D, et al. Identification of heregulin, a specific activator p185erbB2. Science 256, 1205-1210 (1992); 10. Falls D L. Neuregulins: functions, forms and signaling strategies. Experimental Cell Research, 284, 14-30 (2003). 11. Yarden Y, Sliwkowski X. Untangling the ErbB signaling Network. Nature Reviews: Molecular Cell Biology, 2127-137 (2001).
Arrhythmia is due to abnormal excitement of sinoatrial node or excitement out of the sinoatrial node, slow conduction, conduction block or conduction by abnormal channel, namely origin and (or) conduction disorders of heart activity leads to abnormal heart beat frequency and (or) allorhythmia. According to the site of origin, arrhythmia can be divided into sinus arrhythmia, atrial arrhythmia, arrhythmia originated from atrioventricular junction and ventricular arrhythmia. Among them, ventricular arrhythmia is the most common one. Ventricular arrhythmia refers to cardiac arrhythmia originated from ventricule, and includes ventricular premature beat (VPB), ventricular tachycardia (VT) and ventricular fibrillation (VF) etc.
Arrhythmia can be found in a variety of organic heart diseases, more commonly incoronary heart disease (CHD), cardiomyopathy, myocarditis and rheumatic heart disease (RHD), especially in the occurrence of heart failure or acute myocardial infarction. Arrhythmias in generally healthy people, or in patients with autonomic nervous dysfunction are not uncommon. There are other causes such as electrolyte or endocrine disorders, anesthesia, hypothermia, thoracic or cardiac surgery, drug action and diseases of the central nervous system, part with unknown etiology.
Nearly 50 antiarrhythmic drugs have been put into clinical use. So far there is still no unified classification standard. According to the different action mechanism, antiarrhythmic drugs are classified into the following four categories. In order to guide the clinical rational use of drugs, class I drugs are further classified into subtypes A, B and C.    (1) Class I drugs—sodium channel blockers            1) Class I A drugs moderate sodium channel blockade, such as quinindium etc.        2) Class I B drugs mild sodium channels blockade, such as lidocaine etc.        3) Class I C drugs obvious sodium channel blockade, such as flecainide etc.            (2) Class II drugs—β adrenergic receptor blockers    The effect is due to blocking β receptors, and the representative drug is propranolol.    (3) Class III drugs—the drugs prolonging the process of repolarization    This category of drugs includes amiodarone.    (4) Class IV drugs—calcium antagonists    They block the calcium channel and inhibit the internal flow of Ca, and the representative drug is verapamil.
Long term use of antiarrhythmic drugs have different degrees of side effects, thereinto serious side effects are fatal by causing heart block. Ventricular arrhythmia has a high incidence rate, severe prognosis and high risk of long-term drug therapy, the treatment of moderate ventricular arrhythmia, severe ventricular arrhythmia or ventricular arrhythmia accompanied with congestive heart failure (CHF) is very difficult, and many antiarrhythmic drugs cannot be used.
So far, no prior art technical literature has disclosed regulation of ventricular arrhythmia by neuregulin, or effect of neuregulin on ventricular premature beat (VPB), ventricular tachycardia (VT) and ventricular fibrillation (VF) etc.
The present invention found that mammalian neuregulin proteins can greatly reduce or delay the incidence of ventricular arrhythmias and/or ventricular premature beat in patients with heart failure, and may significantly shorten the QTc interval.